Transmitter I/Q mismatch calibration for low if design systems

ABSTRACT

A calibration module includes an absolute value module that generates first and second magnitude signals based on a first signal and a second signal, respectively. A first module generates an amplitude correction signal for a quadrature-amplitude modulated (QAM) signal based on the first and second magnitude signals. A second module generates a phase correction signal for the QAM signal based on the first signal and the second signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/503,044, filed Aug. 11, 2006, now U.S. Pat. No. 7,382,297, whichclaims the benefit of U.S. Provisional Application No. 60/748,484 filedon Dec. 8, 2005. The disclosures of the above applications areincorporated herein by reference in their entirety.

FIELD

The present disclosure relates to correcting amplitude and/or phasemismatch in quadrature amplitude modulation (QAM) mode transmitters.

BACKGROUND

QAM mode transmitters generate a radio frequency (RF) signal that isformed by adding modulated sinusoid and cosine carriers, which are alsoreferred to as in-phase (I) and quadrature (Q) signals, respectively.The I and Q signals can be digitally generated at a lower frequency andthen upconverted to a carrier frequency. The I and Q signals can beupconverted with a pair of analog mixers—one mixer for the I signal andthe other mixer for the Q signal. The analog mixers are generally lessexpensive than their digital counterparts and therefore more popular.

In an ideal case, the amplitudes of the unmodulated I and Q signals areequal and the I and Q signals are exactly 90° out of phase with eachother. However, variances in the analog mixer pairs distort or mismatchthese relationships. The mismatch is referred to as I/Q mismatch. Sincea receiver may incorrectly interpret the I/Q mismatch as an informationsignal, it is important for the transmitter to minimize the I/Qmismatch.

Referring now to FIG. 1, a functional block diagram is shown of anI/Q-mismatch compensated transceiver 10 according to the prior art.Transceiver 10 includes a transmitter section 12, a receiver section 14,and an I/Q mismatch calibration section 16.

Transmitter section 12 includes an I/Q predistortion module 24 thatcompensates the magnitude and/or phase relationship of I and Q signals.The compensation is based on an amplitude correction signal α_(est) anda phase correction signal β_(est), referred to collectively ascorrection signals, that are generated by calibration section 16. I/Qpredistortion module 24 compensates for the I/Q mismatch that may beintroduced by a pair of analog mixers included in an analog transmitter30.

During a calibration sequence, a loopback switch 44 is closed andcouples the output of transmitter section 12 to an input of receiversection 14. Calibration section 16 then measures the I/Q mismatchintroduced by the mixers in analog transmitter 30. Calibration section16 generates the correction signals based on the measurement. I/Qpredistortion module 24 then compensates the magnitude and/or phaserelationship of the I and Q signals to eliminate the I/Q mismatch at theoutputs of analog transmitter 30.

A transmit filter module 26 filters harmonics from the I and Q signals.Outputs of transmit filter module 26 communicate the I and Q signals torespective inputs of a digital-to-analog converter (DAC) 28. DAC 28converts the digital I and Q signals to corresponding analog signals.The analog I and Q signals communicate with respective inputs of analogtransmitter 30.

Receiver section 14 includes an analog receiver 32. Analog receiver 32includes a second pair of analog mixers that regenerate the I and Qsignals from the RF carrier. The second pair of analog mixers introducesadditional I/Q mismatch into the received I and Q signals. Ananalog-to-digital converter (ADC) 36 converts the analog I and Q signalsinto digital I and Q signals. A receive low-pass filter (LPF) 36 filtersharmonic frequencies and communicates the filtered I and Q signals to areceive I/Q compensation module 38. I/Q compensation module 38compensates the digital I and Q signals based on the correction signalsfrom calibration section 16 and compensates for the I/Q mismatch thatwas introduced by analog receiver 32.

Based on a DO_CALIB signal, a demultiplexer 40 routes the compensated Iand Q signals to calibration section 16 or a carrier recovery module 42.The DO_CALIB signal, and a CALIB_MODE signal that is used by ademultiplexer 50, are asserted while transceiver 10 is being calibratedfor I/Q mismatch.

Calibration section 16 includes an I/Q calibrator module 48 thatmeasures the I/Q mismatch between I and Q signals that enter calibrationsection 16. I/Q calibrator module 48 then generates the correctionsignals based on the I/Q mismatch. Based on the CALIB_MODE signal, ademultiplexer 50 then routes the correction signals to transmit I/Qpredistortion module 24 or receive I/Q compensation module 38.

Operation of transceiver 10 will now be described. Transceiver 10supports three operating modes—a receiver calibration mode, atransmitter calibration mode, and a normal operating mode. The I/Qmismatch calibration process begins in the receiver calibration mode.

In the receiver calibration mode loopback switch 44 is opened, a switch46 is closed, and the DO_CALIB and CALIB_MODE signals are set equal to“1”. Switch 46 connects the input of analog receiver 32 to a source 52.Source 52 generates a reference RF carrier that includes ideal I and Qsignals. The analog mixer in analog receiver 32 introduce receiver I/Qmismatch to the ideal I and Q signals. I/Q calibrator module 48 measuresthe receiver I/Q mismatch and based thereon generates the correctionsignals. Demultiplexer 50 routes the correction signals to receive I/Qcompensation block 38. I/Q compensation block 38 stores the correctionsignal values and thereafter compensates the received I and Q signals toeliminate the receiver I/Q mismatch.

Transceiver 10 then enters the transmitter calibration mode. In thetransmitter calibration mode switch 46 is opened, loopback switch 44 isclosed, the DO_CALIB signal is set equal to “1”, and the CALIB_MODEsignal is set equal to “0”. Since receiver section 14 has already beencompensated, I/Q calibrator module 48 can measure the transmitter I/Qmismatch and generate the correction signals for transmitter section 12.Multiplexer 50 routes the correction signals to I/Q predistortion module24. I/Q predistortion module 24 stores the correction signal values andthereafter compensates the I and Q signals to eliminate the transmitterI/Q mismatch. The normal operating mode can then be entered by openingloopback switch 44 and switch 46, and setting the DO_CALIB andCALIB_MODE signals equal to “0”.

Referring now to FIG. 2, a transmitter 60 is shown that employs analternate method of generating the correction signals for I/Qpredistortion module 24. A spectrum analyzer 62 monitors the RF carriersignal while known data signals are communicated into IFFT module 18.Spectrum analyzer 62 then measures the I/Q mismatch introduced by analogtransmitter 30 and generates the correction signals accordingly. I/Qpredistortion module 24 stores the correction signals and compensatesthe I and Q signals accordingly.

The above methods calibrate transmitters 12 and 60 for I/Q mismatch at asingle frequency. The methods can be repeated to calibrate for I/Qmismatch at a number of frequencies. For example, unique correctionsignals can be generated for corresponding RF bands and/or frequenciesused by the Institute of Electrical and Electronics Engineers (IEEE)standards 802.11, 802.11a, 802.11b, 802.11g, 802.11h, 802.11n, 802.16,and 802.20, and/or used by the Bluetooth Special Interest Group (SIG)Bluetooth standard. The aforementioned standards are hereby incorporatedby reference in their entirety. I/Q predistortion module 24 can thenstore the plurality of correction values and use the correction valuesassociated with the carrier frequency being used.

While the above circuits and methods address the issue of I/Q mismatch,they include some undesirable aspects. For example, the method used withtransmitter section 12 is dependent on calibrating receiver section 14.If receiver section 14 is improperly calibrated then the error willadversely affect the correction signals that are generated fortransmitter section 12. Transmitter 60 of FIG. 2 overcomes the issue bycalibrating independently of a receiver section; however it can take anunacceptable amount of time to connect the spectrum analyzer andgenerate the known data signals.

SUMMARY

A calibration module includes a first input that receives a referencesignal, a second input that receives a crosstalk signal, and first andsecond absolute value modules that generate first and second magnitudesignals based on the reference signal and the crosstalk signal,respectively. A first module generates an amplitude correction signalfor a quadrature-amplitude modulated (QAM) signal based on the first andsecond magnitude signals. A second module generates a phase correctionsignal for the QAM signal based on the reference signal and thecrosstalk signal.

In other features the first module employs a difference function. Thesecond module employs a multiplication function. The reference signalincludes a first phase angle. The crosstalk signal is out-of-phase withthe first phase angle. The crosstalk signal is approximately ninetydegrees out-of-phase with the first phase angle.

In other features the calibration module includes first and secondmultiplication modules that multiply the magnitudes of respective onesof the amplitude and phase correction signals. First and second buffersstore the amplitude and phase correction signals, respectively. Thefirst and second buffers include respective inputs and outputs andfurther include feedback paths between the respective inputs and theoutputs. At least one of the feedback paths includes a saturation modulethat limits the magnitude of a feedback signal.

In other features a QAM mode transmitter includes the calibrationmodule. The QAM mode transmitter includes a compensation module thatgenerates compensated in-phase (I) and quadrature (Q) signals based onthe amplitude and phase correction signals; and first and second analogmixers that convert respective ones of the compensated I and Q signalsto a carrier frequency.

A self-calibrating quadrature amplitude modulation (QAM) modetransceiver includes a transmitter. The transmitter includes a generatorthat generates digitized in-phase (I) and quadrature (Q) signals, acompensation module that generates compensated I and Q signals based onthe digitized I and Q signals and amplitude and phase correctionsignals, a digital-to-analog converter module that generates analog Iand Q signals based on the compensated I and Q signals, a first analogmixer module that generates a radio-frequency (RF) transmit signal basedon the analog I and Q signals, and a calibration module that generatesthe amplitude and phase correction signals based on the analog I signalcomponent of the RF transmit signal.

In other features the transceiver includes a receiver. The receiverincludes a second analog mixer module that generates an I componentsignal based on the RF transmit signal. The I component signal includesan analog Q crosstalk signal. An analog-to-digital converter (ADC)converts the I component signal to a digitized I component signal. Adigital mixer generates a reconstructed digitized I signal and adigitized Q crosstalk signal based on the digitized I component signal.The calibration module generates the amplitude and phase correctionsignals based on the reconstructed digitized I signal and the digitizedQ crosstalk signal. The second analog mixer module further generates a Qcomponent signal based on the RF transmit signal. The receiver furthercomprises a band-pass filter (BPF) positioned between the second analogmixer module and the ADC. A switch selectively routes the I componentsignal around the BPF.

A method of calibrating a quadrature-amplitude modulated (QAM) signalincludes receiving a reference signal, receiving a crosstalk signal, andgenerating first and second magnitude signals based on the referencesignal and the crosstalk signal, respectively. The method also includesgenerating an amplitude correction signal for the QAM signal based onthe first and second magnitude signals and generating a phase correctionsignal for the QAM signal based on the reference signal and thecrosstalk signal.

In other features the step of generating the amplitude correction signalemploys a difference function. The step of generating the phasecorrection signal employs a multiplication function. The referencesignal includes a first phase angle and the crosstalk signal isout-of-phase with the first phase angle. The crosstalk signal isapproximately ninety degrees out-of-phase with the first phase angle.The method includes scaling the magnitudes of the amplitude and phasecorrection signals and buffering the amplitude and phase correctionsignals. The amplitude and phase correction signals are bufferedindividually and each buffering step includes generating a feedbacksignal that is input to the buffering step. The method includes limitinga magnitude of the feedback signal.

A method of self-calibrating a quadrature amplitude modulation (QAM)mode transceiver includes generating digitized in-phase (I) andquadrature (Q) signals. The method includes generating compensated I andQ signals based on the digitized I and Q signals and amplitude and phasecorrection signals. The method includes generating analog I and Qsignals based on the compensated I and Q signals, generating aradio-frequency (RF) transmit signal based on the analog I and Qsignals, and generating amplitude and phase correction signals based onthe analog I signal component of the RF transmit signal.

In other features the method includes generating an I component signalbased on the RF transmit signal. The I component signal includes ananalog Q crosstalk signal. The method includes converting the Icomponent signal to a digitized I component signal and generating areconstructed digitized I signal and a digitized Q crosstalk signalbased on the digitized I component signal. The method includesgenerating the amplitude and phase correction signals based on thereconstructed digitized I signal and the digitized Q crosstalk signal.The method includes generating a Q component signals based on the RFtransmit signal. The method includes band-pass filtering the I and Qcomponent signals that are based on the RF transmit signal. The methodincludes selectively routing the I component signal that is based on theRF transmit signal around the band-pass filtering step.

A calibration module includes first input means for receiving areference signal, second input means for receiving a crosstalk signal,and first and second absolute value means for generating first andsecond magnitude signals based on the reference signal and the crosstalksignal, respectively. The calibration module also includes first meansfor generating an amplitude correction signal for a quadrature-amplitudemodulated (QAM) signal based on the first and second magnitude signals;and second means for generating a phase correction signal for the QAMsignal based on the reference signal and the crosstalk signal.

In other features the first means employs a difference function. Thesecond means employs a multiplication function. The reference signalincludes a first phase angle. The crosstalk signal is out-of-phase withthe first phase angle. The crosstalk signal is approximately ninetydegrees out-of-phase with the first phase angle.

In other features the calibration module includes first and secondmultiplication means for multiplying the magnitudes of respective onesof the amplitude and phase correction signals. The calibration moduleincludes first and second buffer means for storing the amplitude andphase correction signals respectively. The first and second buffer meansinclude respective inputs and outputs and respective feedback path meansfor communicating feedback between the outputs and the inputs. At leastone of the feedback paths means includes saturation means for limitingthe magnitude of a feedback signal.

In other features a QAM mode transmitter includes the calibrationmodule. The QAM mode transmitter includes compensation means forgenerating compensated in-phase (I) and quadrature (Q) signals based onthe amplitude and phase correction signals. The QAM mode transmitteralso includes first and second analog mixing means for convertingrespective ones of the compensated I and Q signals to a carrierfrequency.

A self-calibrating quadrature amplitude modulation (QAM) modetransceiver includes a transmitter. The transmitter includes generatormeans for generating digitized in-phase (I) and quadrature (Q) signals,compensation means for generating compensated I and Q signals based onthe digitized I and Q signals and amplitude and phase correctionsignals, digital-to-analog converter means for generating analog I and Qsignals based on the compensated I and Q signals, first analog mixermeans for generating a radio-frequency (RF) transmit signal based on theanalog I and Q signals, and calibration means for generating theamplitude and phase correction signals based on the analog I signalcomponent of the RF transmit signal.

In other features the transceiver includes a receiver. The receiverincludes second analog mixer means for generating an I component signalbased on the RF transmit signal. The I component signal includes ananalog Q crosstalk signal. The receiver also includes analog-to-digitalconverter (ADC) means for converting the I component signal to adigitized I component signal, and digital mixer means for generating areconstructed digitized I signal and a digitized Q crosstalk signalbased on the digitized I component signal. The calibration meansgenerates the amplitude and phase correction signals based on thereconstructed digitized I signal and the digitized Q crosstalk signal.

In other features the second analog mixer means further generates a Qcomponent signal based on the RF transmit signal. The receiver includesa band-pass filter (BPF) means for filtering the I and Q componentsignals communicated from the second analog mixer means to the ADCmodule. The receiver includes switching means for selectively routingthe I component signal around the BPF means.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the disclosure, are intended forpurposes of illustration only and are not intended to limit the scope ofthe disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of a self-calibrating I/Q mismatchcompensated transceiver according to the prior art;

FIG. 2 is a functional block diagram of an I/Q mismatch-compensatedtransmitter according to the prior art;

FIG. 3 is a functional block diagram of an improved self-calibrating I/Qmismatch compensated transceiver;

FIG. 4 is a system diagram of an I/Q calibration module for thetransceiver of FIG. 3;

FIG. 5 is a system diagram of prior art I/Q precompensation module thatcan be used with the transceiver of FIG. 3;

FIG. 6 is a flow chart of a calibration method for the transceiver ofFIG. 3;

FIG. 7A is a functional block diagram of a high definition television;

FIG. 7B is a functional block diagram of a vehicle control system;

FIG. 7C is a functional block diagram of a cellular phone;

FIG. 7D is a functional block diagram of a set top box; and

FIG. 7E is a functional block diagram of a media player.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no wayintended to limit the disclosure, its application, or uses. For purposesof clarity, the same reference numbers will be used in the drawings toidentify similar elements. As used herein, the term module, circuitand/or device refers to an Application Specific Integrated Circuit(ASIC), an electronic circuit, a processor (shared, dedicated, or group)and memory that execute one or more software or firmware programs, acombinational logic circuit, and/or other suitable components thatprovide the described functionality. As used herein, the phrase at leastone of A, B, and C should be construed to mean a logical (A or B or C),using a non-exclusive logical or. It should be understood that stepswithin a method may be executed in different order without altering theprinciples of the present disclosure.

Referring now to FIG. 3, a functional block diagram is shown of anI/Q-mismatch compensated transceiver 100. Transceiver 100 can beimplemented as a system-on-chip (SOC). Transceiver 100 includes atransmitter section 102 and a receiver section 104. Receiver section 104includes an I/Q mismatch calibration module (I/Q-MCM) 106 that generatesan amplitude correction signal α_(est) 105-1 and a phase correctionsignal β_(est) 105-2, collectively referred to as correction signals105. I/Q-MCM 106 generates correction signals 105 based on one of I andQ signals in receiver section 104. I/Q-MCM 106 therefore enablestransmitter section 102 to self-calibrate for I/Q mismatch regardless ofwhether receiver section 104 is I/Q mismatched.

Transmitter section 102 includes an I/Q mismatch precompensation module108 that compensates in-phase (I) and quadrature (Q) signals based oncorrection signals 105. During a calibration mode, which is describedbelow, a reference signal generator 103 generates digitized I and Qsignals. DACs 112 convert the digitized I and Q signals to respectiveanalog I and Q signals.

An analog transmitter 114 includes a first analog mixer 116-1 and asecond analog mixer 116-2. First analog mixer 116-1 generates an Icomponent of the modulated RF carrier by mixing by the analog I signalwith a signal based on the equation cos((ω_(c)−ω_(if))t), where ω_(c)represents the period of the RF carrier, ω_(if) represent the period ofthe IF, and t represents time. Second analog mixer 116-2 generates a Qcomponent of the modulated RF carrier by mixing the analog Q signal witha signal based on the equation sin((ω_(c)−ω_(if))t).

Each analog mixer 116 may have unity gain for amplitude and phase.However, due to variables in material and manufacturing, each analogmixer 116 may have slightly different amplitude and phase gains. Thesedifferent amplitude and phase gains generate an undesirable amplitudedifference α and/or an undesirable phase error β between the I and Qcomponents. The amplitude mismatch α and the phase mismatch β can bemodeled in the mixing signals. The mixing signal for analog mixer 116-1then becomes(1+α/2)cos((ω_(c)−ω_(if))t)+(β/2)  Eq. 1and the mixing signal for analog mixer 116-2 becomes(1−α/2)sin((ω_(c)−ω_(if))t)−β/2)  Eq. 2Eq. 1 is multiplied by the analog I signal to obtain the I component ofthe RF carrier. Likewise, Eq. 2 is multiplied by the analog Q signal toobtain the Q component of the RF carrier. It can be seen from Eqs. 1 and2 that the I and Q components each include information regarding theamplitude mismatch α and the phase mismatch β. I/Q-MCM 106 uses theinformation to generate the correction signals 105 based on equationsthat are described below.

Analog transmitter 114 includes an adder 118 that generates the RFcarrier based on the I and Q components. During I/Q mismatch calibrationthe RF carrier can be looped back, via a loopback switch 120, to aninput of receiver section 104. Loop back switch 120 can be implementedwith a transistor and controlled via a control signal DO_CALIB.

Receiver section 104 includes an analog receiver 122 that receives thelooped-back RF carrier. Analog receiver 122 includes a pair of analogmixers 124-1 and 124-2 that each receive the RF carrier. Analog mixer124-1 reproduces the I component at the IF by mixing the RF carrier witha signal based on the equation cos((ω_(c)−ω_(if))t). Analog mixer 124-2reproduces the Q component at the IF by mixing the RF carrier with asignal based on the equation sin((ω_(c)−ω_(if))t).

During normal operation the reproduced I and Q components communicatethrough respective low-pass filters 125 and switches 126 to respectiveinputs of a complex bandpass filter (BPF) 128. However, during thecalibration mode, the control signal DO_CALIB opens switches 126 andcloses switch 127. Switches 126 and 127 can be implemented withtransistors. Switch 127 selectively connects one of the reproduced I andQ components to an input of a multiplexer 130, bypassing complex BPF128. While FIG. 3 shows one end of switch 127 being connected to theoutput of analog mixer 124-1 it should be appreciated that theconnection can be moved to the output of second mixer 124-2 withoutadversely affecting the operation of transceiver 100.

During the calibration mode multiplexer 130 routes the second end ofswitch 127 to an input of an ADC 132. ADC 132 converts the reproduced Icomponent to a reproduced digital I signal. The reproduced digital Isignal is communicated to a digital mixer 134 that downconverts thereproduced digital I signal from the IF to the baseband frequency.

Digital mixer 134 includes first and second mixers 136-1, 136-2 that mixthe reproduced digital I signal with signals based on the equations cos(ω_(if)t) and sin(ω_(if)t), respectively. The output of first mixer136-1 includes a reproduction of the component I signal. The output ofsecond mixer 136-2 includes a portion of the compensated Q signal. TheQ-signal portion, or crosstalk portion, entered the I component of theRF carrier due to the I/Q mismatch in analog transmitter 114. Thereproduced digital I signal and the crosstalk portion are applied torespective inputs of I/Q-MCM 106. I/Q-MCM 106 then estimates theamplitude mismatch α and the phase mismatch β and generatescorresponding correction signals 105.

I/Q-MCM 106 can employ equations that are included in the followingmathematical derivation. The derivation provides a solution forestimating the amplitude mismatch α and the phase mismatch β based onthe reproduced digital I signal and the crosstalk portion.

The RF carrier signal that is received by analog receiver 122 can bedescribed by the equation:S _(RF)=(1+α/2)I cos(ω_(c) t+β/2)+(1−α/2)Q sin(ω_(c) t−β/2)  Eq. 3The reproduced I component at the output of analog mixer 124-1 can thenbe described by the equation:I _(IF) =I[cos((2ω_(c)+ω_(if))t)+cos(ω_(c)t)]+Q[sin((2ω_(c)−ω_(if))t)+sin(ω_(if) t)]  Eq. 4LPFs 125 diminish signals at frequencies above the IF and the reproducedI component at the output of LPF 125-1 can then be described by thesimplified equation:

$\begin{matrix}{\begin{matrix}{I_{IF} = {\left( S_{RF} \right){\cos\left( {\left( {\omega_{c} - \omega_{if}} \right)t} \right)}}} \\{= {\left( {1 + {\alpha/2}} \right)❘{{\cos\left( {{\omega_{if}t} + {\beta/2}} \right)} + {\left( {1 - {\alpha/2}} \right)Q\;{\sin\left( {{\omega_{if}t} - {\beta/2}} \right)}}}}}\end{matrix}\mspace{40mu}\begin{matrix}{{Eq}.\mspace{14mu} 5} \\{{Eq}.\mspace{14mu} 6}\end{matrix}} & \;\end{matrix}$

The reproduced digital I signal at the output of first mixer 136-1 canbe described by the equation:

$\begin{matrix}{I_{BB} = {\left( I_{IF} \right){\cos\left( {\omega_{if}t} \right)}}} \\{= {{\left( {1 + {\alpha/2}} \right)I\;{\cos\left( {\beta/2} \right)}} - {\left( {1 - {\alpha/2}} \right)Q\;{\sin\left( {\beta/2} \right)}}}}\end{matrix}\mspace{130mu}\begin{matrix}{{Eq}.\mspace{14mu} 7} \\{{Eq}.\mspace{14mu} 8}\end{matrix}$

The crosstalk portion at the output of second mixer 136-2 can bedescribed by the equation:Q _(BB)=(1+α/2)I sin((β/2)−(1−α/2)Q cos(β/2)  Eq. 9Eq. 9 assumes that signal components at 2 ω_(if) are removed by LPF125-1.

I_(BB) and Q_(BB) are communicated to respective inputs of I/Q-MCM 106,which estimates ∫(I_(BB) ²−Q_(BB) ²) and ∫I_(BB)×Q_(BB). Using Eq. 8 andEq. 9,

$\begin{matrix}{{I_{BB}^{2} - Q_{BB}^{2}} = {{\left( {1 + {\alpha/2}} \right)^{2}I^{2}{\cos^{2}\left( {\beta/2} \right)}} + {\left( {1 - {\alpha/2}} \right)^{2}Q^{2}{\sin^{2}\left( {\beta/2} \right)}} -}} \\{{2\left( {1 - {\alpha^{2}/4}} \right){IQ}\;\sin\;{\beta/2}} - \left\lbrack {{\left( {1 + {\alpha/2}} \right)^{2}I^{2}{\sin^{2}\left( {\beta/2} \right)}} +} \right.} \\\left. {{\left( {1 - {\alpha/2}} \right)^{2}Q^{2}{\cos^{2}\left( {\beta/2} \right)}} - {2\left( {1 - {\alpha^{2}/4}} \right){IQ}\;\sin\;{\beta/2}}} \right\rbrack \\{= {{\left( {1 + {\alpha/2}} \right)^{2}{I^{2}\left( {{\cos^{2}\left( {\beta/2} \right)} - {\sin^{2}\left( {\beta/2} \right)}} \right)}} -}} \\{\left( {1 - {\alpha/2}} \right)^{2}{Q^{2}\left( {{\cos^{2}\left( {\beta/2} \right)} - {\sin^{2}\left( {\beta/2} \right)}} \right)}} \\{= {\left\lbrack {I^{2} + {\alpha\; I^{2}} + {{\alpha^{2}/4}I^{2}} - Q^{2} + {\alpha\; Q^{2}} - {{\alpha^{2}/4}Q^{2}}} \right\rbrack\left( {\cos\;\beta} \right)}} \\{= {\left\lbrack {{\left( {I^{2} - Q^{2}} \right)\left( {1 - {\alpha^{2}/4}} \right)} + {\alpha\left( {I^{2} + Q^{2}} \right)}} \right\rbrack\cos\;\beta}}\end{matrix}$

Noting that I=cos(ω_(BB)t) and Q=sin(ω_(BB)t),

∫₀^(T)(I² − Q²) 𝕕t = 0, ∫₀^(T)(I² + Q²) 𝕕t = T, ∫₀^(T)IQ 𝕕t = 0.

It can also be assumed that β is small. Hence cos β=1 and α<<1. Henceα²/4≈0. Thus

$\begin{matrix}{{\int_{0}^{T}{\left( {I_{BB}^{2} - Q_{BB}^{2}} \right)\ {\mathbb{d}t}}} = {{T\;\alpha} = {{constant} \times \alpha}}} & {{Eq}.\mspace{14mu} 10}\end{matrix}$

Now considering ₀∫^(T)I_(BB)Q_(BB)dt,

$\begin{matrix}{{I_{BB}Q_{BB}} = {{\left( {1 + {\alpha/2}} \right)^{2}I^{2}\sin\;{\beta/2}} + {\left( {1 - {\alpha/2}} \right)^{2}Q^{2}\sin\;{\beta/2}} -}} \\{\left( {1 - {\alpha^{2}/4}} \right){I/{Q\left( {{\cos^{2}\left( {\beta/2} \right)} + {\sin^{2}\left( {\beta/2} \right)}} \right)}}} \\{= {{\sin\;{\beta/{2\left\lbrack {I^{2} + {\alpha\; I^{2}\alpha^{2}{I^{2}/4}} + Q^{2} - {\alpha\; Q^{2}\alpha^{2}{Q^{2}/4}}} \right\rbrack}}} - \left( {1 - {\alpha^{2}/4}} \right)}} \\{I/Q}\end{matrix}$

From the above assumption that β is small,

$\begin{matrix}{{\int_{0}^{T}{I_{BB}Q_{BB}\ {\mathbb{d}t}}} = {{T\;\beta} = {{constant} \times \beta}}} & {{Eq}.\mspace{14mu} 11}\end{matrix}$I/Q-MCM 106 can therefore employ Eq. 10 and Eq. 11 to estimate theamplitude mismatch α and the phase mismatch β respectively and generatecorresponding correction signals 105.

Referring now to FIG. 4, a functional block diagram is shown of I/Q-MCM106. A first input 201 receives the reproduced digital I signal andcommunicates with an input of a first absolute value module 202. Anoutput of first absolute value module 202 communicates with an input ofa summation module 204. An output of summation module 204 communicateswith an input of a scaling module 206. Scaling module 206 provides again of 2^(stePI), where stepI is an integer less than or equal to zero.An output of scaling module 206 communicates with an input of asummation module 208. Summation module 208 communicates instantaneousestimates of the amplitude mismatch a to a buffer 210. Buffer 210generates α_(est) 105-1 and communicates α_(est) 105-1 to an output andto an input of a saturation filter 211. α_(est) 105-1 is a signed binaryinteger and saturation filter 211 prevents α_(est) 105-1 from rollingover after it saturates. An output of saturation filter 211 communicateswith a second input of summation module 208.

A second input 213 receives the crosstalk portion and communicates withan input of a second absolute value module 212 and an input of amultiplication module 214. An output of second absolute value module 212communicates with a second input of summation module 204. First input201 communicates with a second input of multiplication module 214. Anoutput of multiplication module 214 communicates with an input of ascaling module 216. Scaling module 216 provides a gain of 2^(stePQ),where stepQ is an integer less than or equal to zero. An output ofscaling module 216 communicates with an input of a summation module 218.Summation module 218 communicates instantaneous values of the phasemismatch 13 to a buffer 220. Buffer 220 generates p est 105-2 andcommunicates β_(est) 105-2 to an output and to an input of a saturationfilter 221. β_(est) 105-2 is a signed binary integer and saturationfilter 221 prevents β_(est) 105-2 from rolling over after it saturates.An output of saturation filter 221 communicates with a second input ofsummation module 218.

Referring now to FIG. 5, a functional block diagram is shown of an I/Qmismatch precompensation module 108. It should be appreciated that otherimplementations may also be used. A first input 250 receives the ideal Isignal. A buffer 252 buffers the ideal I signal and communicates it toan input of a multiplication module (global) 254. Multiplication module254 also receives α_(est) 105-1. An output of multiplication module 254communicates with an inverting input of a summation module 256. A secondinput of summation module 256 receives the ideal I signal from theoutput of buffer 252. An output of summation module 256 communicateswith an input of a summation module 258. A second input 260 receives theideal Q signal. A buffer 262 buffers the ideal Q signal and communicatesit to an input of a multiplication module 264. A second input ofmultiplication module 264 receives β_(est) 105-2. An output ofmultiplication module 264 communicates with an inverting input ofsummation module 258. An output of summation module 258 communicatesinstantaneous values of the compensated I signal to a buffer 268. Anoutput of buffer 268 generates the compensated I signal.

An input of multiplication module 270 receives the ideal Q signal fromthe output of buffer 262. A second input of multiplication module 270receives α_(est) 105-1. An output of multiplication module 270communicates with an input of a summation module 272. A second input ofsummation module 272 receives the ideal Q signal from the output ofbuffer 262. An output of summation module 272 communicates with an inputof a summation module 274. A multiplication module 276 receives theideal I signal from the output of buffer 252 and receives β_(est) 105-2.An output of multiplication module 276 communicates with an invertinginput of summation module 274. An output of summation module 274communicates instantaneous values of the compensated Q signal to aninput of a buffer 278. An output of buffer 278 generates the compensatedQ signal.

Referring now to FIG. 6 a method of calibrating the transmitter section102 of transceiver 100 is shown. The method can be implemented ascombinatorial logic and executed when transceiver 100 is turned on.Control enters through a start block 302 and proceeds to block 304. Inblock 304 control enables reference signal generator 103 to communicatethe ideal I and Q signals to the respective inputs of I/Q mismatchprecompensation module 108. Control then proceeds to block 306 andupconverts the compensated I and Q signals to the carrier frequency viaanalog mixers 116. Control then proceeds to block 308 and closesloopback switch 120 to route the RF carrier signal to the input ofanalog receiver 122. Control then proceeds to block 310 and opensswitches 126 and closes switch 127 to bypass the reproduced I componentaround complex BPF128. Control then proceeds to block 312 and convertsthe reproduced I signal to the digital domain via ADC 132. Control thenproceeds to block 314 and converts the reproduced I component to thebaseband frequency via first digital mixer 136-1. In block 314 controlalso generates the crosstalk component of the reproduced I component viasecond digital mixer 136-2. Control then proceeds to block 316 andestimates the amplitude mismatch α and phase mismatch β based on Eqs. 10and 11 respectively. Control then proceeds to block 318 and generatescorrection signals 105 based on the estimated amplitude mismatch α andthe phase mismatch β. Control then pre-compensates the I and/or Qsignals in transmitter section 102. Control then proceeds to otherprocesses via exit block 320.

Referring now to FIGS. 7A-7G, various exemplary implementations of theI/Q-mismatch compensated transceiver are shown. Referring now to FIG.7A, the I/Q-mismatch compensated transceiver can be implemented in ahigh definition television (HDTV) 420. The I/Q-mismatch compensatedtransceiver may implement and/or be implemented in a wireless local areanetwork (WLAN) and/or wireless personal area network (WPAN) interface429. An example of a WPAN includes a Bluetooth network. The HDTV 420receives HDTV input signals in either a wired or wireless format andgenerates HDTV output signals for a display 426. In someimplementations, signal processing circuit and/or control circuit 422and/or other circuits (not shown) of the HDTV 420 may process data,perform coding and/or encryption, perform calculations, format dataand/or perform any other type of HDTV processing that may be required.

The HDTV 420 may communicate with mass data storage 427 that stores datain a nonvolatile manner such as optical and/or magnetic storage devices.Mass data storage 427 may include a digital versatile disc (DVD) driveand/or a mini hard disc drive (HDD). The HDD can include one or moreplatters having a diameter that is smaller than approximately 1.8″. TheHDTV 420 may be connected to memory 428 such as RAM, ROM, low latencynonvolatile memory such as flash memory and/or other suitable electronicdata storage. The HDTV 420 also may support connections with a WLANand/or WPAN via the interface 429. HDTV 420 may include a power supply423.

Referring now to FIG. 7B, the I/Q-mismatch compensated transceiver mayimplement and/or be implemented in a WLAN and/or WPAN interface 448 of avehicle 430. Vehicle 430 includes a powertrain control system 432 thatreceives inputs from one or more sensors such as temperature sensors,pressure sensors, rotational sensors, airflow sensors and/or any othersuitable sensors and/or that generates one or more output controlsignals such as engine operating parameters, transmission operatingparameters, and/or other control signals.

A control system 440 may likewise receive signals from input sensors 442and/or output control signals to one or more output devices 444. In someimplementations, the control system 440 may be part of an anti-lockbraking system (ABS), a navigation system, a telematics system, avehicle telematics system, a lane departure system, an adaptive cruisecontrol system, a vehicle entertainment system such as a stereo, DVD,compact disc and the like. Still other implementations are contemplated.

The powertrain control system 432 may communicate with mass data storage446 that stores data in a nonvolatile manner. The mass data storage 446may include optical and/or magnetic storage devices, such as, HDDsand/or DVDs. One or more of the HDDs may be a mini HDD that includes oneor more platters having a diameter that is smaller than approximately1.8″. The powertrain control system 432 may be connected to memory 447such as RAM, ROM, low latency nonvolatile memory such as flash memoryand/or other suitable electronic data storage. The powertrain controlsystem 432 also may support connections with a WLAN and/or WPAN via theinterface 448. The control system 440 may also include mass datastorage, memory and/or a WLAN and/or WPAN interface (all not shown).Vehicle 430 may also include a power supply 433.

Referring now to FIG. 7C, the I/Q-mismatch compensated transceiver canbe implemented in a cellular phone 450 that may include a cellularantenna 451. The I/Q-mismatch compensated transceiver may implementand/or be implemented in a WLAN and/or WPAN interface 468. In someimplementations, the cellular phone 450 includes a microphone 456, anaudio output 458 such as a speaker and/or audio output jack, a display460 and/or an input device 462 such as a keypad, pointing device, voiceactuation and/or other input device. The signal processing and/orcontrol circuits 452 and/or other circuits (not shown) in the cellularphone 450 may process data, perform coding and/or encryption, performcalculations, format data and/or perform other cellular phone functions.

The cellular phone 450 may communicate with mass data storage 464 thatstores data in a nonvolatile manner such as optical and/or magneticstorage devices for example HDDs and/or DVDs. One of more of the HDDsmay be a mini HDD that includes one or more platters having a diameterthat is smaller than approximately 1.8″. The cellular phone 450 may beconnected to memory 466 such as RAM, ROM, low latency nonvolatile memorysuch as flash memory and/or other suitable electronic data storage. Thecellular phone 450 also may support connections with a WLAN and/or WPANvia the interface 468. Cellular phone 450 may also include a powersupply 453.

Referring now to FIG. 7D, the I/Q-mismatch compensated transceiver canbe implemented in a set top box 480. The I/Q-mismatch compensatedtransceiver may implement and/or be implemented in a WLAN and/or WPANinterface 496. The set top box 480 receives signals from a source suchas a broadband source and outputs standard and/or high definitionaudio/video signals suitable for a display 488 such as a televisionand/or monitor and/or other video and/or audio output devices. Thesignal processing and/or control circuits 484 and/or other circuits (notshown) of the set top box 480 may process data, perform coding and/orencryption, perform calculations, format data and/or perform any otherset top box functions.

The set top box 480 may communicate with mass data storage 490 thatstores data in a nonvolatile manner. The mass data storage 490 mayinclude optical and/or magnetic storage devices, such as, HDDs and/orDVDs. One or more of the HDDs may be a mini HDD that includes one ormore platters having a diameter that is smaller than approximately 1.8″.The set top box 480 may be connected to memory 494 such as RAM, ROM, lowlatency nonvolatile memory such as flash memory and/or other suitableelectronic data storage. The set top box 480 also may supportconnections with a WLAN and/or WPAN via the interface 496. The set topbox 480 may also include a power supply 483.

Referring now to FIG. 7E, the I/Q-mismatch compensated transceiver canbe implemented in a media player 500. The I/Q-mismatch compensatedtransceiver may implement and/or be implemented in a WLAN and/or WPANinterface 516. In some implementations, the media player 500 includes adisplay 507 and/or a user input 508 such as a keypad, touchpad and thelike. In some implementations, the media player 500 may employ agraphical user interface (GUI) that typically employs menus, drop downmenus, icons and/or a point-and-click interface via the display 507and/or user input 508. The media player 500 further includes an audiooutput 509 such as a speaker and/or audio output jack. The signalprocessing and/or control circuits 504 and/or other circuits (not shown)of the media player 500 may process data, perform coding and/orencryption, perform calculations, format data and/or perform any othermedia player functions.

The media player 500 may communicate with mass data storage 510 thatstores data such as compressed audio and/or video content in anonvolatile manner. In some implementations, the compressed audio filesinclude files that are compliant with MP3 format or other suitablecompressed audio and/or video formats. The mass data storage 510 mayinclude optical and/or magnetic storage devices, such as, HDDs and/orDVDs. One or more of the HDDs may be a mini HDD that includes one ormore platters having a diameter that is smaller than approximately 1.8″.The media player 500 may be connected to memory 514 such as RAM, ROM,low latency nonvolatile memory such as flash memory and/or othersuitable electronic data storage. The media player 500 also may supportconnections with a WLAN and/or WPAN via the interface 516. The mediaplayer 500 may also include a power supply 513. Still otherimplementations in addition to those described above are contemplated.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the disclosure can beimplemented in a variety of forms. Therefore, while this disclosureincludes particular examples, the true scope of the disclosure shouldnot be so limited since other modifications will become apparent to theskilled practitioner upon a study of the drawings, the specification andthe following claims.

1. A method for compensating a transmit signal comprising at least twomodulated carriers, the method comprising: mixing a first modulatedcarrier of the at least two modulated carriers with a firstpredetermined signal to reproduce a first component of the transmitsignal at an intermediate frequency; converting the first component ofthe transmit signal to a corresponding digital signal; mixing thedigital signal with a second predetermined signal to reproduce the firstcomponent of the transmit signal at a baseband frequency; mixing thedigital signal with a third predetermined signal to reproduce a portionof a second component of the transmit signal at the baseband frequency;and estimating an amplitude mismatch and a phase mismatch between the atleast two modulated carriers of the transmit signal based on (i) thefirst component of the transmit signal at the baseband frequency and(ii) the portion of the second component of the transmit signal at thebaseband frequency.
 2. The method of claim 1, wherein the mixing of thefirst modulated carrier of the at least two modulated carriers with thefirst predetermined signal comprises mixing the first modulated carrierwith a signal based on cos((ω_(c)−ω_(if))t), where ω_(c) represents aperiod of the first modulated carrier, ω_(if) represent a period of theintermediate frequency, and t represents time.
 3. The method of claim 2,wherein: the mixing of the digital signal with the second predeterminedsignal comprises mixing the digital signal with a signal based oncos(ω_(if)t); and the mixing of the digital signal with the thirdpredetermined signal comprises mixing the digital signal with a signalbased on sin(ω_(if)t).
 4. The method of claim 1, wherein the estimatingof the amplitude mismatch and the phase mismatch between the at leasttwo modulated carriers of the transmit signal comprises employing one ormore of (i) a difference function or (ii) a multiplication function. 5.The method of claim 1, wherein the transmit signal comprises aquadrature-amplitude modulated (QAM) signal.
 6. The method of claim 1,wherein the estimating of the amplitude mismatch and the phase mismatchbetween the at least two modulated carriers of the transmit signalcomprises scaling one or more of (i) a magnitude of the amplitudemismatch or (ii) a magnitude of the phase mismatch.
 7. The method ofclaim 1, further comprising generating a compensated transmit signalbased on (i) the estimated amplitude mismatch and (ii) the estimatedphase mismatch between the at least two modulated carriers.
 8. Atransceiver comprising: an analog mixer configured to mix a firstmodulated carrier of at least two modulated carriers with a firstpredetermined signal to reproduce a first component of a transmit signalat an intermediate frequency; an analog-to-digital converter configuredto convert the first component of the transmit signal to a correspondingdigital signal; a first digital mixer configured to mix the digitalsignal with a second predetermined signal to reproduce the firstcomponent of the transmit signal at a baseband frequency; a seconddigital mixer configured to mix the digital signal with a thirdpredetermined signal to reproduce a portion of a second component of thetransmit signal at the baseband frequency; and a calibration moduleconfigured to estimate an amplitude mismatch and a phase mismatchbetween the at least two modulated carriers of the transmit signal basedon (i) the first component of the transmit signal at the basebandfrequency and (ii) the portion of the second component of the transmitsignal at the baseband frequency.
 9. The transceiver of claim 8, whereinthe first predetermined signal is based on cos((ω_(c)−ω_(if))t), whereω_(c) represents a period of the first modulated carrier, ω_(if)represent a period of the intermediate frequency, and t represents time.10. The transceiver of claim 9, wherein: the second predetermined signalis based on cos(ω_(if)t); and the third predetermined signal is based onsin(ω_(if)t).
 11. The transceiver of claim 8, wherein the transmitsignal comprises a quadrature-amplitude modulated (QAM) signal.
 12. Thetransceiver of claim 8, further comprising a pre-compensation moduleconfigured to generate a compensated transmit signal based on (i) theestimated amplitude mismatch and (ii) the estimated phase mismatchbetween the at least two modulated carriers.
 13. A system comprising thetransceiver of claim
 8. 14. The system of claim 13, wherein the systemcomprises one of a high definition television, a vehicle, a cellularphone, a set top box, or a media player.
 15. A calibration module,comprising: an absolute value module configured to generate (i) a firstmagnitude signal based on a first component signal and (ii) a secondmagnitude signal, based on a second component signal; a first moduleconfigured to generate an amplitude correction signal for aquadrature-amplitude modulated (QAM) signal based on (i) the firstmagnitude signal and (ii) the second magnitude signal; and a secondmodule configured to generate a phase correction signal for the QAMsignal based on (i) the first component signal and (ii) the secondcomponent signal.
 16. The calibration module of claim 15, wherein thefirst module employs a difference function.
 17. The calibration moduleof claim 16, wherein the second module employs a multiplicationfunction.
 18. The calibration module of claim 15, wherein the firstsignal includes a first phase angle, wherein the second signal isout-of-phase with the first phase angle.
 19. The calibration module ofclaim 18, wherein the second signal is approximately ninety degreesout-of-phase with the first phase angle.
 20. The calibration module ofclaim 15, further comprising a multiplication module configured tomultiply magnitudes of respective ones of the amplitude correctionsignal and the phase correction signal.
 21. The calibration module ofclaim 15, further comprising a buffer configured to store the amplitudecorrection signal and the phase correction signal.
 22. The calibrationmodule of claim 21, wherein the buffer includes inputs and outputs, andfurther comprising feedback paths between the inputs and the outputs.23. The calibration module of claim 22 wherein at least one of thefeedback paths includes a saturation module configured to limitmagnitude of a feedback signal.
 24. A QAM mode transmitter comprisingthe calibration module of claim
 15. 25. The QAM mode transmitter ofclaim 24, further comprising: a compensation module configured togenerate a compensated in-phase (I) signal and a compensated quadrature(Q) signal based on the amplitude correction signal and the phasecorrection signal; a first analog mixer; and a second analog mixer,wherein the first analog mixer is configured to convert the compensatedI signal to a carrier frequency, and wherein the second analog mixer isconfigured to convert the compensated Q signal to the carrier frequency.26. A method of calibrating a quadrature-amplitude modulated (QAM)signal, comprising: generating a first magnitude signal based on a firstcomponent signal; generating a second magnitude signal based on a secondcomponent signal; generating an amplitude correction signal for the QAMsignal based on the first magnitude signal and the second magnitudesignal; and generating a phase correction signal for the QAM signalbased on the first component signal and the second component signal. 27.The method of claim 26, wherein the generating of the amplitudecorrection signal employs a difference function.
 28. The method of claim26, wherein the generating of the phase correction signal employs amultiplication function.
 29. The method of claim 26, wherein the firstcomponent signal includes a first phase angle and the second componentsignal is out-of-phase with the first phase angle.
 30. The method ofclaim 29, wherein the second component signal is approximately ninetydegrees out-of-phase with the first phase angle.
 31. The method of claim26, further comprising scaling magnitudes of the amplitude correctionsignal and the phase correction signal.
 32. The method of claim 26,further comprising buffering the amplitude correction signal and thephase correction signal.
 33. The method of claim 32, wherein: theamplitude correction signal is buffered via a first buffer to generate afirst feedback signal; and the phase correction signal is buffered via asecond buffer to generate a second feedback signal.
 34. The method ofclaim 33, further comprising limiting magnitudes of the first feedbacksignal and the second feedback signal.
 35. The method of claim 1,further comprising receiving the at least two modulated carriers via areceiver, wherein: the mixing of the first modulated carrier of the atleast two modulated carriers with the first predetermined signal isperformed subsequent to the receiving of the at least two modulatedcarriers; and the mixing of the digital signal with the secondpredetermined signal is performed by the receiver and subsequent to themixing of the first modulated carrier of the at least two modulatedcarriers with the first predetermined signal.
 36. The method of claim 1,wherein the mixing of the digital signal with the second predeterminedsignal and the mixing of the digital signal with the third predeterminedsignal include downconverting frequency of the digital signal to thebaseband frequency.
 37. The method of claim 1, wherein the portion ofthe second component is a crosstalk portion of the first componentcorresponding to component mismatch in the transmit signal.